Problem: Simplify the following expression: $n = \dfrac{r}{8} - \dfrac{10r}{3}$
Answer: In order to subtract expressions, they must have a common denominator. The smallest common denominator is the least common multiple of $8$ and $3$ $\lcm(8, 3) = 24$ $ n = \dfrac{3}{3} \cdot \dfrac{r}{8} - \dfrac{8}{8} \cdot \dfrac{10r}{3} $ $n = \dfrac{3r}{24} - \dfrac{80r}{24}$ $n = \dfrac{3r -80r}{24}$ $n = \dfrac{-77r}{24}$